1. Field of the Invention
Aspects of the present invention relate to a printing apparatus that includes an inkjet print head.
2. Description of the Related Art
In an inkjet printing apparatus, a sheet passing quickly under a print head absorbs moisture in the air. Consequently, the ink discharge nozzles in the print head dry more quickly, which can cause problems with printing, such as ink clogging of the nozzles.
Regarding this issue, Japanese Patent Application Laid-Open No. 2011-121354 discusses a printing apparatus that includes a mechanism for suppressing the sheet from absorbing moisture below the print head by humidifying the sheet before it reaches the print head. In the apparatus discussed in Japanese Patent Application Laid-Open No. 2011-121354, the moisture content of the sheet is increased by supplying a humidified gas onto the sheet from a first supply port. In addition, a humidified gas is supplied from a second supply port, which is located closer to the print head than the first supply port, into a space where the nozzles of the print head are exposed. Based on this mechanism, the humidity of the space where the nozzles are exposed is maintained so that the nozzles retain their moisture.
Some printing apparatuses include a mechanism for heating the sheet before printing, such as a decurling mechanism that corrects curl by applying heat onto the sheet. In such an apparatus, because the sheet is hot, the sheet does not sufficiently absorb moisture even if a humidified gas is supplied onto the sheet before printing, as is discussed in Japanese Patent Application Laid-Open No. 2011-121354. This is because for a sheet having high hygroscopicity such as paper, the higher the temperature of the sheet, the less moisture that the sheet can absorb. In other words, the lower the temperature of the sheet, the greater the amount of moisture that the sheet can absorb.
If a sheet is fed to a printing unit at a high temperature but without sufficient moisture absorption, the hygroscopicity of the sheet increases due to a decrease in the sheet temperature during that time, so that a lot of the humidity is taken from the space where the nozzles are exposed in the print head. Consequently, problems can occur with printing due to the nozzles becoming dry.